The present invention refers to an apparatus for and method of restoring a damaged area of a coating of a drum, with the coating applied through hot vulcanization and the damaged area being essentially filled by a patch which is connectable to the drum body.
Such drums with a coating usually made of rubber is widely used. During operation, the coating progressively wears off so that the drum has to be re-coated after a certain period. This requires a detachment of the drum from the respective machine.
Apart from such progressive wear, the coating may also become only partially damaged. Such partially damaged areas could theoretically be patched up without necessitating a complete re-coating of the drum because despite such locally damaged areas, the overall performance of the drum could still meet the requirements.
It is known to mend damaged areas through insertion of a patch and to connect the patch with the drum body through cold vulcanization. However, the surface finish of the drum body remains unsatisfactory after such repair, thus adversely affecting the quality of a material web transported through the drum. A reason for that resides in the different material composition of the patch which is applied through cold bonding or cold vulcanization, on the one hand, and the original coating which is bonded with the drum body through hot vulcanization, on the other hand.
Especially in drum electrodes which are part of an arrangement for corona treatment and perform a corona discharge on advancing material webs, 8 the quality of the material web surface is considerably reduced because the different application of the patch and the coating will result in an uneven corona discharge.
In order to avoid these problems, the occurrence of damaged coating areas generally requires a complete replacement of the drums and subsequently a complete re-coating thereof. This, however, is very uneconomic. In particular a replacement of drums in sheet stretching plants or of drums used in the paper industry is very time consuming and complicated because of the considerable size and weight of such drums.